EYE SCLEROTIC COAT. 445 



The Mucous membrane of the nasal fossa? is called pituitary, or Sclmd- 

 derian* The former name being derived from the nature of its secretion, 

 the latter from Schneider, who was the first to show that the secretion of 

 the nose proceeded from the mucous membrane, and not from the brain, 

 as was formerly imagined. It is continuous with the general gastro-pul- 

 monary mucous membrane, and may be traced through the openings in 

 the meatuses, into the sphenoidal and ethmoidal cells ; into the frontal 

 sinuses ; into the antrum maxillare ; through the nasal duct to the surface 

 of the eye, where it is continuous with the conjunctiva ; along the Eusta- 

 chian tubes into the tympanum and mastoid cells, to which it forms the 

 lining membrane ; and through the posterior nares into the pharynx and 

 mouth, and thence through the lungs and alimentary canal. 



The surface of this membrane is furnished with a columnar epithelium 

 supporting innumerable vibratile cilia. 



Ve&wls and Nerves. The Arteries of the nasal fossae are the anterior 

 and posterior ethmoidal, from the ophthalmic artery; and the spheno- 

 palatine and ptery go-palatine from the internal maxillary. 



The Nerves are, the olfactory, the spheno-palatine branches from Meckel's 

 ganglion, and the nasal branch of the ophthalmic. The ultimate filaments 

 of the olfactory nerve terminate in papillae. 



THE EYE, WITH ITS APPENDAGES. 



The form of the eyeball is that of a sphere, of about one inch in diame- 

 ter, having the segment of a smaller sphere engrafted upon its anterior 

 surface, which increases its antero-posterior diameter. The axes of the 

 two eyeballs are parallel with each other, but do not correspond with the 

 axes of the orbits, which are directed outwards. The optic nerves follow 

 the direction of the orbits, and therefore enter the eyeballs to their nasal 

 side. 



The Globe of the Eye is composed of tunics, and of refracting media 

 called humours. The tunics are three in number, the 



1. Sclerotic and Cornea, 



2. Choroid, Iris, and Ciliary processes, 



3. Retina and Zonula ciliaris. 



The humours are also three 



Aqueous, 

 Crystalline (lens)^ 

 Vitreous. 



FIRST TUNIC. The Sclerotic and Cornea form the external tunic of the 

 eyeball, and give it its peculiar form. Four-fifths of the globe are invested 

 by the sclerotic, the remaining fifth by the cornea. 



The Sclerotic (<fx\vifa, hard) is a cense fibrous membrane, thicker behind 

 than in front. It is continuous, pos teriorly, with the sheath of the optic 

 nerve, which is derived from the du ra mater, and is pierced by that ner"fi 

 as well as by the ciliary nerves ai d arteries. Anteriorly it presents a 

 bevelled edge which receives the c urnea in the same way that a watcn- 



Conrad Victor Schneider, profes?or of} fedicine a,. WY'tenberg. His work, entitled 

 De Catarrhis, &c. was published in 1 >CJ. 



38 



